A selective absorption phenomenon observable in a wide variety of polycrystalline compounds containing nonspherical atomic nuclei when placed in a magnetic radio-frequency field. Nuclear quadrupole resonance (NQR) is very similar to nuclear magnetic resonance (NMR), and was originated in the late 1940s by H. G. Dehmelt and H. Krüger as an inexpensive (no stable homogeneous large magnetic field is required) alternative way to study nuclear moments.